Phase inversion circuit



May 7, 1957 INVENTOR. JOHN R. K0585 United States Patent PHASE tNvEnsioN CIRCUIT John R. Kobbe, Beaverton, Oreg, assignor to Tektronix, Inc., Portland, Greg, a corporation of Qregon Application July 6, 1953, Serial No. 366,211

4 Ciaims. (Ci. 179--171) This invention relates to phase inversion circuits.

It is a main object of the present invention to provide a phase inversion circuit utilizing two phase inverting tubes having their cathodes directly connected together, wherein the grid of one tube is eifectively connected to a common conductor and input signals are impressed between the grid of the other tube and such conductor, and wherein there is voltage dividing means for the input signals including another tube having series resistance in its cathode circuit providing a connecting point at which the signal voltage is substantially half the input signal voltage and to which the cathodes of the phase inverting tubes are directly connected.

The particular embodiment of the invention disclosed in the drawing and to be described in detail hereinafter is particularly and uniquely adapted for inverting video signals, but the invention is not limited to this particular application since phase inverting circuits embodying the basic concepts of the invention may be employed for inverting audio signals and in other circuits which will be apparent to those skilled in the art once the concepts of the present invention are revealed.

It is a more particular object of the present invention to provide a phase inversion circuit of the type generally indicated above wherein the voltage dividing means provides a low impedance circuit for supplying signals to the cathodes of the phase inverting tubes.

It is a further particular object of the present invention to, provide a phase inversion circuit of the type indicated above wherein the voltage dividing means can be arranged for applying signals of exactly one half the value of the original input signals to the cathodes of the phase inverting tubes to obtain completely balanced phase inversion.

Various other objects of the present invention will be apparent from the following description taken in connection with the accompanying drawing wherein the single figure shows a diagram of a circuit embodying the concepts of the present invention.

Referring to the accompanying drawing, it is apparent that there are three tubes 9, 11 and 13, tubes 11 and 13 having their cathodes connected by a conductor 15 and constituting the phase inverting tubes of the circuit. The plate of tube 11 is connected through a resistance 17 to a source of positive voltage, and the pla-te of tube 13 is also connected through a resistance 19 to such source of positive voltage. Preferably resistances 17 and 19 are made of the same value.

In the particular circuit shown, the tubes 11 and '13 are pentodes, wherein the screens are connected directly to the source of positive voltage supply. Trio'des or tetrodes could be utilized instead of pentodes if desired.

Output conductors 21 and 23 are connectedto the plates of tubes 11 and 13, and are adapted to supply signals to other circuit-s. It is assumed that the loads to which conductors 21 and 23 are connected are equal, although they may be unequal if desired. Conductors '21 and 23 could be, for instance, connected to a suitable amplifier for supplying voltages to the vertical-defiection plates of a cathode ray oscilloscope.

Tube 11 has its grid connected through a conductor 25 to the grid of the tube 9, whereas the grid of tube 13 is connected to ground.

The tube 9 has series resistance in its cathode circuit and signals are impressed between its grid and ground through a conductor 27 containing a coupling condenser 29, there being a grid resistor 31 connecting the grid of tube 9 to ground. Conductor 25, feeding signals to the grid of tube 11, is directly connected to conductor 27; therefore, tubes 9 and 11 have identical signals impressed on their grids.

The cathode of tube 9 is connected by a conductor 33 and an adjustable resistor 35 to a conductor 15 which connects the cathodes of tubes 11 and 13. Conduct-or 15 is connected to ground through a conductor 37 and a fixed resistor 39.

If exactly balanced out-of-phase outputs from the plates of tubes 11 and 13 are desired, the following relationship is established. The effective resistance for signal voltages between =the grid and cathode of tube 9 plus the resistance value of resistor 35 is made equal to the resistance value of resistor 39. This relationship may be established by adjusting the value of resistor 35. Also, tubes 11 and 1 3 are selected so that they have similar electrical characteristics. It follows that, with the above relationships, a voltage divider for alternating or transient voltages is provided between the grid of tube 9 and ground, where one half the resistance of the voltage divider is between conductor 15 and the grid of the cathode follower 9 and the other half of the resistance of the voltage divider is between conductor 15 and ground. Thus, a signal of one half the value of the signal impressed between conductor 25 and ground will be developed between conductor 15 and ground. Consequently, the difference in potential betwen the grid'of tube 11 and its cathode will be one half the value of the input signal and, since the grid of tube 13 is grounded, the signal between its cathode and grid is one half the original signal. Since the signal voltages between the grids and cathodes of tubes 11 and 13 are identical, but of inverse relationship, the outputs from the two tubes must be equal, but, of course, out of phase.

it the input signal is a positive pulse, the grid of tube 11 will obviously be driven in a positive direction relative to its cathode and thus the plate current output from tube 11 will increase, whereas the rise in voltage on line 15, and therefore of the cathode of tube 13, will have the same efiect on tube 13 as if the grid of said tube were driven in a negative direction relative to its cathode, and therefore the plate current output of tube 13 will decrease. Thus, phase inversion results and, because of the voltage dividing arrangement above set forth, this phase inversion will produce equal though out-of-phase outputs from the two tubes.

in the circuit shown in the drawing, the plate signal voltage of: the tube 13 may be made to exceed that of the tube 11, by reducing the value of resistance 35 discussed above. With such an arrangement, the signal voltage between conductor 15 and ground will be greater than one half the value of the signal between conductor 25 and ground, and therefore the plate signal voltage of tube 11 Will decrease, and the plate signal voltage of tube 13 will increase, the decrease of plate signal voltage of tube 11 being substantially equal to the increase of plate signal voltage of tube 13. Thus, the signal output of tube 13 will be greater than the signal output of tube 11.

By the above circuit, it is apparent that exact balance or out-of-balance outputs from tubes 11 and 13 may be obtained by increasing or decreasing the value or resistance 35. It is also apparent that resistor 35jrnay be entirely eliminated and a balanced output achieved by making resistor 39 have a value equal to the effective resistance for signal voltages between the grid and cathode of tube 9. Also, a greater signal output from tube 13 than tube 11 may be obtained by eliminating resistor 35 and making the value of resistor 39 greater than such effective resistance. it will also be observed that the signal output of tube 11 may be made to exceed that of tube 13 by merely making resistor 39 have a value less than the value of resistor 35 plus such effective resistance.

The circuit of the present invention has fast wide'band response because, apart from coupling condenser 29, which does not enter into the time constant of the phase inverting circuit, the capacitance of the circuit comprises only interelectrode and stray capacitances, and the tube components are resistance coupled to one another and to ground by resistances which can be made to have very low values, such as, for instance, 100 or 200 ohms. Thus, the R-C time of the circuit is very small.

Having illustrated and described a preferred embodi ment of the invention, it should be apparent to those skilled in the art that the invention permits of modification in arrangement and detail. I claim as my invention all such modifications as come within the true spirit and scope of the appended claims.

What I claim as my invention is:

1. A phase inverting circuit comprising an electron discharge tube having an anode, a cathode and a control grid, cathode connection means for connecting said cathode to a common conductor, means for connecting said anode to a source of positive potential with respect to said conductor, means for impressing an input signal voltage between said grid and said conductor, said cathode connection means containing series resistance and having a connection point at which the signal voltage with respect to said conductor is substantially one half said input signal voltage, second and third electron discharge tubes similar to each other and each having an anode, a cathode and a control grid, means for connecting said anodes of each of said second and third tubes through similar load resistors to a source of positive potential with respect to said conductor, said cathodes of said second and third tubes being directly connected to each other and to said connection point, grid connection means for each of said second and third tubes for maintaining each of said grids of said second and third tubes at a negative bias voltage with respect to said cathodes of said second and third tubes, said grid connection means for said second tube including means for impressing between said grid of said second tube and said conductor a signal voltage substantially equal to said input signal voltage and said grid connection means for said third tube ineluding means for maintaining said grid of said third tube at substantially zero signal voltage with respect to said conductor so as to produce at the anodes of said second and third tubes signal voltages with respect to said conductor which are substantially equal and of opposite phase.

2. A phase inverting circuit comprising an electron discharge tube having an anode, a. cathode and a control grid, cathode connection means for connecting said cathode to ground, means for connecting said anode to a source of positive potential with respect to ground, means for impressing an input signal voltage between said grid and ground, said cathode connection means containing series resistance and having a connection point at which the signal voltage with respect to ground is substantially one half said input signal voltage, second and third electron discharge tubes similar to each other and each having an anode, a cathode and a control grid, means for connecting said anodes of each of said second and third tubes through similar load resistors to a source of positive potential with respect to ground, said cathodes of said second and third tubes being directly connected to each other and to said connection point, grid connection means for each of said second and third tubes for maintaining each of said grids of said second and third tubes at a negative bias voltage with respect to said cathodes of said second and third tubes, said grid connection means for said second tube including means for impressing between said grid of said second tube and ground a signal voltage substantially equal to said input signal voltage and said grid connection means for said third tube including means for maintaining said grid of said third tube at substantially zero signal voltage with respect to ground so as to produce at the anodes of said second and third tubes signal voltages with respect to ground which are substantially equal and of opposite phase.

3. A phase inverting circuit comprising an electron discharge tube having an anode, a cathode and a control grid, cathode connection means for connecting said cathode to a common conductor, means for connecting said anode to a source of po'stive potential with respect to said conductor, means for impressing an input signal voltage between said grid and said conductor, said cathode connection means containing a pair of resistors in series and having a connection point between said resistors, one of said resistors being adjustable to provide a signal voltage at said point with respect to said conductor which is substantially one half said input signal voltage, second and third electron discharge tubes similar to each other and each having an anode, a cathode and a control grid, means for connecting said anodes of each of said second and third tubes through similar load resistors to a source of positive potential with respect to said conductor, said cathodes of said second and third tubes being directly connected to each other and to said connection point, grid connection means for each of said second and third tubes for maintaining each of said grids of said second and third tubes at a negative bias voltage with respect to said cathodes of said second and third tubes, said grid connection means for said second tube including means for impressing between said grid of said second tube and said conductor a signal voltage substantially equal to said input signal voltage and said grid connection means for said third tube including means for maintaining said grid of said third tube at substantially zero signal voltage with respect to said conductor so as to produce at the anodes of said second and third tube signal voltages with respect to said conductor which are substantially equal and of opposite phase.

4. A phase inverting circuit comprising an electron discharge tube haviug an anode, a cathode and a control grid, cathode connection means for connecting said cathode to ground, means for connecting said anode to a source of positive potential with respect to ground, means for impressing an input signal voltage between said grid and ground, said cathode connection means containing series resistance and having a connection point at which the signal voltage with respect to ground is substantially one half said input signal voltage, second and third electron diseharge tubes similar to each other and each having an anode, a cathode and a control grid, means for connecting said anodes of each of said second and third tubes through similar load resistors to a source of positive potential with respect to ground, said cathodes of saidsecond and third tubes being directly connected to each other and to said connection point, grid connection means for each of said second and third tubes for maintaining each of said grids of said second and third tubes at a negative bias voltage with respect to said cathodes of said second and third tubes, said grid connection means for said second tube including a grid resistor between said grid of said second tube and ground and means for impressiug'between said grid of said sec-0nd tube and ground a signal voltage substantially equal to said input signal voltage and said grid connection means for said third tube directly connecting said grid of said third tube toground 5 1 so as to produce at the anodes of said second and third tubes signal voltages with respect to ground which are substantially equal and of opposite phase.

References Cited in the file of this patent UNITED STATES PATENTS Bourget Nov. 18, 1952 

